In systems such as mobile communication systems, radar systems etc., it is sometimes of interest to suppress radiation of signal power in certain directions. The reason for doing this in e.g. a mobile communication system is typically to reduce interference and, thus, improve system performance.
A typical property of an antenna is that, in the main lobe direction, crosspolar components are significantly suppressed in comparison with copolar components, whereas, in side lobe directions, the crosspolar components may be of the same magnitude as the copolar components. This means that when a null is formed in a certain direction or angular region on the basis of the copolar components, the depth of that null will be limited by the crosspolar components.